User manual

Page 73
EA Elektro-Automatik GmbH
Helmholtzstr. 31-33 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
[e-mail]
PSI 9000 DT Series
3.10 Other applications
3.10.1 Series connection
Series connection of two or multiple devices is basically possible, but for reasons of safety and isolation following
restrictions apply:
• Both, negative (DC-) and positive (DC+) output poles are coupled to PE via type X capacitors,
limiting the max. allowed potential shift (see technical specs for rating)
• Remote sensing must not be connected!
• Series connection is only allowed with devices of the same kind and model, i.e. power supply
with power supply like, for instance, PSI 9080-60 DT with PSI 9080-60 DT
Series connection is not explicitly supported by additional connections and signals on the devices. Nothing else
than output current and voltage is shared. It means, all units have to be controlled separately regarding set values
and DC output status, whether it is manual or remote control.
According to the limit of the potential shift that comes with series connection (also see section „2.3.6. Grounding of
the DC output“), models with a certain nominal output voltage must not be connected in series at all. For example
the 750 V model, because there the DC minus is only isolated up to ±400 V DC against PE. On the opposite, two
360 V units are allowed to be connected in series.
The analog interfaces of units in series connection are allowed to be wired in parallel, because they are galvanically
isolated from the device and the DC output. The grounds (AGND, DGND) on the analog interface are also allowed
to be directly connected to PE, like it automatically happens when controlling and directly connecting it to a PC.
3.10.2 Parallel operation
Multiple devices of same kind and ideally same model can be connected in parallel in order to create a system
with higher total current and hence higher power. This can be achieved by connecting all units to the DC load in
parallel, so the single currents can add. There is no support for a balancing between the individual units, like in
form of a master-slave system. All power supplies would have to be controlled and set up separately. However,
it is possible to have a parallel control by the signals on the analog interface, as this one is galvanically isolated
from the rest of the device. There are few general points to consider and adhere:
• Always make parallel connections only with device of same voltage, current and power rating
• Never connect the ground signal of any analog interface with the negative DC output, because it will void the
galvanic isolation. This rule is especially important when going to connect any DC output pole to ground (PE)
or to shift its potential.
• Never connect DC cables from power supply to power supply, but instead from every power supply device directly
to the load, else the total current will exceed the current rating of the DC output clamp
3.10.3 Operation as battery charger
A power supply can be used as a battery charger, but with some restrictions, because it misses a battery super-
vision and a physical separation from the load in form of a relay or contactor, which is usually featured with true
battery chargers as a protection against overvoltage or reversed polarity.
Following has to be considered:
• No false polarity protection inside! Connecting a battery with false polarity will damage the power supply severely,
even if it is not powered.
• All models of this series have an internal circuit, i.e. base load, for faster discharge of voltage when switching the
DC output off or ramping voltage down. This base load would, more or less slowly, discharge the battery while
the DC output is switched off, means while it is not charging. This would, however, not occur when the power
supply is not powered at all. It is thus recommended to leave the DC output switched on as long as the battery
is connected (equals to trickle charge) and only switch if off for connecting/disconnecting a battery.